What Is Vig?
Before we talk parlays, quick refresher on vig (short for vigorish, also called "juice"). When a sportsbook posts a line like -110/-110 on both sides of a bet, they're building in their profit margin. You risk $110 to win $100 — that extra $10 is the vig.
On a standard -110/-110 market, the house edge works out to roughly 4.5%. That means for every $100 wagered across all bettors, the book expects to keep about $4.55. On a single bet, that's a small tax. The problem starts when you stack those bets into a parlay.
How Vig Compounds in Parlays
Each leg you add to a parlay multiplies the vig from every other leg. It's not addition — it's compounding, like interest working against you. Here's how the effective house edge grows as you add legs (assuming standard -110 odds on each):
| Legs | Effective House Edge | Your Implied Win % |
|---|---|---|
| 1 | ~4.5% | ~52.4% |
| 2 | ~9% | ~27.5% |
| 3 | ~13% | ~14.4% |
| 4 | ~17% | ~7.5% |
| 5 | ~21% | ~3.9% |
| 6 | ~24% | ~2.1% |
| 7 | ~28% | ~1.1% |
| 8 | ~31% | ~0.5% |
| 9 | ~34% | ~0.3% |
| 10 | ~37% | ~0.1% |
| 11 | ~40% | ~0.06% |
By the time you reach a 6-leg parlay, roughly a quarter of the theoretical payout is being eaten by the vig. At 11 legs, 40% of your expected payout is gone before the games even start. And that's on even-money bets. Sprinkle in a few heavy favorites and it gets worse.
The Math
Let's walk through a simple 2-leg parlay where both sides are -110.
Each -110 leg has a true probability of 50% (a coin flip). If you bet two independent coin flips, your true odds of winning both are 0.50 × 0.50 = 25%. At fair odds, a 25% chance should pay +300 (risk $100 to win $300).
But the sportsbook doesn't pay +300 on a 2-leg parlay of -110 picks. They pay around +264. That gap — +300 vs. +264 — is the compounded vig. You're getting shortchanged roughly $36 per $100 wagered compared to fair odds.
Scale that up: a 4-leg parlay of -110 picks should pay +1500 at true odds. Books pay closer to +1228. That's nearly $272 in vig on a $100 bet. The more legs, the wider the gap between what you should get paid and what you actually get paid.
Why Books Push Parlays
Ever notice how sportsbooks are aggressively promoting parlays? There's a reason — they're the most profitable product the book offers. Here's how they push them:
- Same-Game Parlays (SGPs): These are marketed as a fun way to "build your own bet" within a single game. What they don't advertise is that SGP legs are often correlated, which lets the book adjust the odds even further in their favor. The vig on SGPs is typically higher than on traditional parlays because the book has more latitude to set the combined price however they want.
- Parlay Insurance: "Get your money back if one leg loses!" Sounds generous, but the refund is usually a bonus bet (worth less than cash), and the existence of the insurance is already priced into the odds you're getting.
- Boost Promotions: Profit boosts on parlays can be worthwhile — but only if the boost actually exceeds the compounded vig. We break down exactly how much boost you need for every leg count in our parlay profit boosts guide.
The bottom line: if the book is advertising it aggressively, it's because it's usually profitable for them. Do the math before assuming a promo is a good deal.
When Parlays Make Sense
Parlays aren't always a bad bet. There are specific situations where they can be smart:
Correlated Parlays That Books Misprice
When two outcomes are genuinely linked, a parlay can capture value that straight bets can't — if the book doesn't fully adjust for the correlation. Traditional multi-game parlays assume independence between legs, but same-game parlays are where the real opportunities show up.
Here's a real-world example: for a long stretch, BetMGM didn't properly account for the correlation between assists and rebounds in their NBA SGP pricing. A player who grabs 10+ rebounds and dishes 10+ assists in the same game is, by definition, flirting with a triple-double. But you could build a 2-leg SGP of "10+ rebounds" and "10+ assists" on certain players and get paid significantly more than the same book's triple-double prop — even though the SGP was essentially a subset of the same outcome. The book's SGP algorithm treated the legs as more independent than they actually are, and the mispricing was exploitable for months.
That's the kind of edge to look for: outcomes that are clearly correlated in real life but that the book's model prices as if they're mostly independent. Other examples include parlaying a team to win with the under (dominant defensive teams), or a quarterback's passing yards with his team's total points. When you spot one, the parlay vig might be more than offset by the correlation discount you're getting.
Promos That Offset the Vig
Stepped-up profit boost promos can genuinely overcome the compounded vig — but not all of them do. The key is knowing the exact breakeven boost percentage for your number of legs and comparing it to what the book is offering. We built a full breakeven table and walk through how to evaluate any promo in our parlay profit boosts guide.
Small-Stake Entertainment
If you're betting $5 on a 4-leg parlay for fun on a Sunday afternoon, the expected loss is small in dollar terms. Just know that you're paying a premium for the excitement.
The Takeaway
Every leg you add to a parlay is more edge for the sportsbook. On standard -110 lines, the vig compounds with each leg — a 2-leg parlay costs you ~9%, a 4-legger ~17%, and an 11-leg parlay gives up a staggering 40% of your expected payout before the games even start.
Keep it simple. Straight bets are the sharpest play in sports betting. If you're going to parlay, make sure you've found a real correlation the book is mispricing or a profit boost that genuinely exceeds the breakeven threshold — otherwise, you're just paying extra for the thrill.
